Modern day manufacturing plants process, treat, inspect, segregate, transport, and otherwise handle articles or objects at extremely high speeds. Many such applications require the reliable detection and counting of relatively fast moving objects. For example, newspaper publishing plants typically deliver signatures to the mail room at the rate of 80,000 per hour or more, for purposes of being formed into signature bundles of an accurate, predetermined count, which bundles are then wrapped or tied and delivered to various locations for sale or subsequent delivery.
Many of the articles have distinctive profiles that may be used for detection purposes. In the present example, the signatures are typically delivered in an overlapping stream with folded edges forward. The folded forward edges have typically been utilized for counting and stacking purposes. Counters of the mechanical or optical type are typically employed for counting articles, such as signatures, in the stream by simply and accurately identifying the passage of the folded forward edge or the nose of a signature. However, mechanical signature counters have the disadvantage of wearing after prolonged use. Optical systems become degraded due to the accumulation of dust or dirt on the optical components.
It is therefore desirable to provide a method and apparatus for detecting and counting which does not experience wearing suffered by mechanical counters and which does not become degraded due to accumulation of foreign matter upon the sensing elements as is the case with counters of the optical type.